The present invention pertains to transmission of supervision data between PCM switching systems and more particularly to circuitry for reformatting the supervision data to a form readily accessible and useable by a central processing unit which controls a switching system.
In a per-channel signaling arrangement for PCM data transmission, the least significant bit of particular data samples is utilized to transmit supervisory data. Typically, digital span data is transmitted in a unit termed a time frame. The time frame includes a synchronization bit and 24 channels of PCM information. Each channel is an 8-bit representation of a particular PCM data sample.
A collection of 12 time frames is termed a super time frame. During the 6th and 12th time frames of each super time frame, the least significant bit of each channel is deleted. In place of this deleted bit, supervision data is included. The supervision data transmitted is an A supervision bit and a B supervision bit. During the 6th time frame of each super time frame, an A supervision bit is inserted into the least significant bit of each channel. During the 12th time frame of each super frame, a B supervision bit is inserted into the least significant bit position of each channel.
The switching system that receives the supervision data must detect and store this data. Typically, this supervision information (the A and B supervision bits) is stored one channel (one supervision bit) per address location. This is ideal for processing by the switching network. However, it is undesirable for software scanning since it would take 192 read operations to scan the supervisory status of each of the channels of up to 8 digital spans.
Accordingly, it is the object of the present invention to provide a PCM supervision data reformatting circuit which orders the supervision data such that, a minimum number of CPU memory accesses may be made to examine the supervision data.